This present invention relates generally to check valves for keeping fluid from traveling in a reverse direction and more specifically, to a check valve having a variable opening-force threshold.
Backflow check valves are typically utilized in fluid-carrying pipelines to prevent the backflow or return of downstream fluids, such as from service lines or main supply lines. Such backflow check valves are commonly situated between the main supply line and a facility""s (school, home, etc.) service line. Examples of such check valves may be found by reference to U.S. Pat. No. 6,050,293 to Lin et al., U.S. Pat. No. 3,789,874 to Hills, U.S. Pat. No. 4,887,792 to Kuo, U.S. Pat. No. 3,482,603 to Outcalt and U.S. Pat. No. 3,334,858 to Hay.
Though Hills, Kuo, Outcalt, and Hay all disclose a check valve assembly for backflow prevention in pipelines, their designs are disadvantageous in light of the present invention. All of the aforementioned devices require a specific predetermined threshold fluid pressure to initially open the check valve, and thereafter, require the fluid pressure to remain relatively constant, if not greater, to maintain the check valve in an open position. A decrease in fluid pressure often results in check valve xe2x80x9cflutterxe2x80x9d and the associated signature noise, wherein the flutter noise is caused by the valve plate flapping back and forth due to the lack of requisite pressure to maintain the check valve in a consistently open position. Furthermore, none of the aforementioned devices incorporate into their design the ability to allow opening of the check valve upon variance of fluid flow threshold.
Therefore, it is readily apparent that there is a need for a check valve having a variable opening force threshold, wherein the check valve requires a relatively larger initial forward flow pressure to open the check valve but thereafter requires a relatively smaller forward-flow pressure to keep the check valve in an open position, thereby reducing check valve xe2x80x9cflutterxe2x80x9d and allowing closure of the check valve upon the ceasing of forward flow and/or the initiation of backflow.
Briefly described, in a preferred embodiment, the present invention overcomes the above-mentioned disadvantages and meets the recognized need for such a device by providing a check valve with variable opening force threshold, wherein the check valve requires a relatively large initial forward-flow pressure to open the check valve but thereafter, only requires a relatively small forward-flow pressure to maintain the check valve in an open position. As such, the present invention reduces check-valve flutter and allows closure of the valve upon backflow or if forward flow is reduced below a predetermined minimum threshold.
According to its major aspects and broadly stated, the present invention in its preferred form is a check valve generally comprising a check-valve assembly having a mounting member, a buttress, a valve seat, a valve plate, a pivotable cam arm, a pivotable closure arm and a follower wheel.
More specifically, the present invention is a check valve having a mounting member to secure the check-valve assembly into a body such as a pipeline. The mounting member preferably includes a mounting section, a valve seat section and a buttress, wherein the buttress carries a flapper assembly, a pivotable cam arm and a pivotable closure arm. The flapper assembly generally has a valve plate and a plate cap. The valve plate is attached to the pivotable cam arm. The pivotable cam arm includes a hump forming a cam surface opposite the valve plate. A follower wheel attached to the pivotable closure arm rests on the cam surface of the hump. When a forward flow of fluid pushes against the plate cap, the follower wheel of the pivotable closure arm must first overcome the hump of the pivotable cam arm to open the valve. Upon reaching a predetermined opening threshold pressure, the pivotable closure arm is sufficiently loaded that the attached follower wheel overcomes the cam hump thus allowing the valve to fully open. Thereafter, only minimal force is required to maintain the valve in an open position due to the contour of the remainder of the cam surface.
A feature and advantage of the present invention is the novel and unique initial opening-force threshold of the device.
A feature and advantage of the present invention is the ability of the check valve, after reaching the initial opening-force threshold, to remain open with relatively slow fluid flow or minimum pressure.
A feature and advantage of the present invention is the ability of the check valve to remain open with relatively slow fluid flow yet still avoid check valve flutter commonly associated with such conditions.
A feature and advantage of the present invention is that the hump on the pivotable cam arm can be varied in size, shape and slope to adjust the overall performance of the check valve relative to the initial forward flow force and thus create a suitable check valve for any fluid flow conditions.
A feature and advantage of the present invention is its ability to be incorporated into any environment where prevention of fluid backflow is desired.